As more software functions move to the Internet, where the traditional software licensing business model has limitations, companies are experimenting with new business models such as subscriptions and advertising-supported software.

Microsoft is trying it with its Works suite, which comes standard -- and free to the user -- on many new computers. Likewise, Google Docs and Spreadsheets -- online versions of the productivity apps dominated by Microsoft -- are advertising supported. Now Adobe, a leader in rich Internet applications with its Flash player and nearly ubiquitous PDF reader and writer, is getting into the act with help from Yahoo.

On Thursday, the companies announced a partnership to allow publishers to serve contextual ads into PDF documents. Like all of these early ad-funded software efforts, this is a test program for starters and it's opt-in.

From the release: "The new service allows publishers to generate revenue by including contextual, text-based ads next to Adobe PDF content, with Yahoo! providing access to its extensive network of advertisers to match a broad range of subject matter. For advertisers, Ads for Adobe PDF Powered by Yahoo! extends reach by delivering advertising across a new channel of content, while also providing the ability to track advertising performance, just as they can today with ads placed on Web sites."

The program will open up new real estate for its advertisers, according to Todd Teresi, svp of Yahoo!'s publisher network, especially among small-time customers that don't even have Web sites. Example: Local youth soccer leagues that create weekly e-mail newsletters could generate funds through contextual placements for soccer equipment and jerseys -- and even minivans, he said.

"The primary users long term are going to be down the tail," Teresi said.

The program is offered as a free service to US-based publishers who produce English content. Early adopters include IDG InfoWorld, Wired, Pearson's Education, Meredith Corporation and Reed Elsevier.